1. Field of the Invention
The present invention relates to an apparatus for suppressing interference in wireless telecommunications systems, and in particular to an apparatus and method for suppressing frequency interference occurring between a transmitting device and a receiving device in a mobile telecommunication system.
2. Description of the Related Art
A cellular mobile telecommunication system allows a subscriber to communicate with other subscribers. The entire service area is divided into a plurality of cells having a corresponding base station. The base stations are centralized by a mobile switching center.
The cellular mobile telecommunication system is divided into an analog cellular system and a digital cellular system. The AMPS (Advanced Mobile Phone System) functions as the analog cellular system and the CDMA (Code Division Multiple Access) or the FDMA (Frequency Division Multiple Access) system function as the digital cellular system.
Due to the rapid and exponentional growth of mobile telecommunications, a plurality of users use limited frequency resources, particularly in cities. Hence, two or more systems using different communication methods may be located adjacent to each other. Therefore, the frequency separation between the systems becomes narrow and frequency interference inevitably occurs between the systems.
Consequently, the transmit frequency and receive frequency of two signals adjacent to each other and corresponding to two different systems are not sufficiently apart from each other, thereby causing interference which can significantly affect voice quality. Generally, the output signal and interference signals of a system using one particular communication method or protocol causes degradation in the receiving capability of the other system using a different communication method. The interference condition is typically dealt with by limiting frequency allocation or by adjusting a radiation pattern of the transmitting antenna. Another conventional method is to incorporate a transmit band pass filter (TBPF) in the transmitting system to pass only a transmit frequency band and to incorporate a receive band pass filter (RBPF) in the receiving system to pass only a receive frequency band.
However, conventional methods do not completely suppress frequency interference when the transmit frequency of a system is close proximity with the receive frequency of another system, because the TBPF and RBPF can not completely isolate the out-of-band signals.
The band pass filters, which are used in the mobile telecommunication system, include a band pass filter to pass the in-band frequency and a notch filter to maximally reduce the out-of-band frequency interference. However, the filter has a larger insertion loss than the band pass filter, and therefore may adversely affect system performance. Additionally, the noise attenuation characteristics in the band where the out-of-band frequency is apart within 1 Mega-Hertz (MHz) cannot obtain effects better than the general band pass filter. Therefore, in circumstances where the transmit frequency of a system is in close proximity with the receive frequency of another system, it has been generally required to do something more than to add a notch filter for solving the problem of frequency interference.
U.S. Pat. No. 4,535,476 discloses an offset geometry, interference canceling receiver which performs interference cancellation by the dither signal frequency and a round trip signal delay. The apparatus solves the problem of frequency interference by coupling an antenna to cancellation circuits via several duplexer and amplifier circuit combinations. However, the apparatus cannot suppress frequency interference occurring between different systems in proximity to each other.
The present invention provides an apparatus and method for suppressing frequency occurring between different communication systems. An apparatus and method for suppressing frequency occurring between different communication systems are provided. The apparatus and method suppress frequency interference by providing a reflecting assembly in proximity to a transmitting antenna.
In the case where frequency of a first signal causes interference with a frequency of a second signal, where the frequency of the first signal is transmitted from a transmit antenna of a first communication system and the frequency of the second signal is received by a receive antenna of a second communication system in proximity to the first communication system, the apparatus of the present invention includes: a reflecting assembly for reducing the incoming interference signal from the transmit antenna to the receive antenna, wherein the reflecting assembly is equipped to the transmit antenna of the first communication system; and an adjusting assembly operatively associated with the reflecting assembly to adjust the position of the reflecting assembly. The position is adjusted by varying the slope of the reflecting assembly, by moving the reflecting assembly right and left, and by changing the height of the reflecting assembly.
The reflecting assembly includes a plurality of lattices, where a gap is defined between each of the plurality of lattices having a width of xcex/N, where xcex is the wavelength of the first signal and N is a natural number. The reflecting assembly includes two reflecting panes made from aluminum and symmetric about the adjusting assembly. The width of each of the reflecting panes is equal to the length of the transmit antenna.
The method of the present invention suppresses frequency interference where a frequency of a first signal causes interference with a frequency of a second signal, the first signal being transmitted from a transmit antenna of a first communication system, the second signal being received by a receive antenna of a second communication system in proximity to the first communication system. The method comprises the steps of: providing a reflecting assembly for reducing the incoming interference signal from the transmit antenna to the receive antenna, the reflecting assembly being equipped to the transmit antenna of said first communication system; and adjusting the position of the reflecting assembly to suppress the frequency interference.
The present invention suppresses frequency interference when the transmit and receive antennas of a telecommunications system have a narrow frequency separation and are located in proximity to each other.